Evaluation of four α-diketones for toll-like receptor-4 (TLR-4) activation in a human transfected cell line

Food Chem Toxicol. 2014 Dec;74:117-9. doi: 10.1016/j.fct.2014.09.010. Epub 2014 Oct 2.

Abstract

Toll-like receptor-4 (TLR-4) activity is upregulated in persons with fibrotic lung diseases secondary to chronic inflammatory conditions like Crohn's disease and rheumatoid arthritis. We hypothesized that α-diketones associated with fixed obstructive lung disease may activate TLR-4. We utilized a human embryonic kidney cell assay (HEK293) with human TLR-4 receptors to test for potential activation effects of 2,3-butandeione, 2,3-pentanedione, 2,3-hexanedione, and 2,3-heptanedione at test concentrations of 1, 10, 100, and 1000 µM. The assay detects NF-κB-induced expression of secreted alkaline phosphatase measured after 16 h incubation by a UV-VIS Spectrometer at 650 nm. Escherichia coli K12 lipopolysaccharide (LPS) at 0.5 ng/mL served as a positive control and was added with each test compound to evaluate combined effects. None of the tested α-diketones were found to exhibit cytotoxicity, agonism, or synergistic effects with LPS in the human TLR-4 assay up to 1000 µM. Screening of 2,3-butanedione for agonist activity using the HEK assay with mouse TLR-4 receptors exhibited cytotoxicity at 1000 µM, but no agonist activity. We conclude that the tested α-diketones at relatively high concentrations in vitro do not exhibit TLR-4 agonist or synergistic activity and, therefore, apparently do not directly induce inflammasome activation through this pathway in humans or mice.

Keywords: Bronchiolitis obliterans; Diacetyl; Fibrotic lung disease; Humans; Inflammasome.

MeSH terms

  • Diacetyl / pharmacology*
  • Dose-Response Relationship, Drug
  • HEK293 Cells / drug effects
  • Hexanones / pharmacology*
  • Humans
  • Ketones / pharmacology*
  • Pentanones / pharmacology*
  • Toll-Like Receptor 4 / antagonists & inhibitors
  • Toll-Like Receptor 4 / drug effects*
  • Up-Regulation / drug effects

Substances

  • Hexanones
  • Ketones
  • Pentanones
  • TLR4 protein, human
  • Toll-Like Receptor 4
  • 2,3-hexanedione
  • Diacetyl
  • 2,3-pentanedione